Knowledgebase : GMail App
smtp plugins do not send emails via G suite or gmail accounts

1. Check your login and password

2. Allow less secure apps to access your account

3. Enable IMAP and POP for G Suite

4. Use ASP or unlock Captcha

error sending emails to gmail based email - 552 5.2.3 our size gu...

error sending emails to gmail based email - 552 5.2.3 our size guidelines

With Gmail, you can send and receive messages up to 25 megabytes (MB) in size.

Read more:

In English
https://support.google.com/mail/bin/answer.py?hl=en&answer=8770&rd=1

In Russian
http://productforums.google.com/forum/#!topic/gmail-ru/p0ZrKf6P8Vg 

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